This invention is directed to thermoplastic compositions having an improved balance of modulus and impact strength and, in particular, to thermoplastic compositions comprising a copolyestercarbonate, and articles prepared therefrom.
Polycarbonates are amorphous polymers noted for their optical properties, thermal resistance, toughness, and impact resistance. High flow polycarbonates, polyesters, and other polymers, typically those having low molecular weights and are available for the injection molding of parts with very thin dimensions and long flow lengths.
Copolyestercarbonate, having both ester and carbonate repeat units, are known to have polycarbonate-like properties together with substantially increased flow at the same molecular weight as an ordinary aromatic polycarbonate. EP 0510 958 B1 and U.S. Pat. No. 5,605,980, for example, disclose a composition, comprising a bisphenol-A-copolyestercarbonate having dodecanedioate content, exhibiting improved melt flow compared to polycarbonates of the same molecular weights. EP 0510 958 B1 does not disclose examples of compositions comprising polyesters, impact modifiers, fillers, or fluoropolymers.
In order to obtain desirable flow properties, however, the impact strength of the polycarbonate and other mechanical properties (elongation at break or the like) can be compromised. Thin-wall and complex injection molded parts with minimal residual stress and low temperature ductility are, therefore, not readily prepared from existing polycarbonate materials.
WO 2008/063724 discloses blends of a polyester with at least two different copolyester carbonates, which comprise arylate ester units. Blends of polyesters and polycarbonates are also known. An alloy or blend of polyester with polycarbonate can offer some improvements with respect to the properties of polycarbonates. For example, alloys of a polycarbonate, a polyester such as polyalkylene terephthalate, and an emulsion-ABS graft copolymer are disclosed in U.S. Pat. No. 7,067,567. This patent discloses a flame resistant polymer composition containing no chlorine or bromine elements and improved weld line strength for molding.
U.S. Patent Publications 2005/0143508 A1 and 2006/0142455 A1 describe particular polymer compositions that give optimum balance of mechanical properties, especially high modulus combined with good ductility and impact strength. These compositions contain a matrix polymer component and a combination of fluoropolymer and mineral filler. US Patent Publications 2008/0242789 A1 and 2008/0246181 A1 describe specific polymer compositions containing a blend of polyesters and polycarbonates and a combination of mineral filler and fluoropolymer, which again have an optimum balance of impact and modulus.
It would be desirable to obtain thermoplastic compositions having a superior balance of modulus and impact properties combined with retention of its flow characteristics to retain processability. Modification of the molecular weights of the thermoplastic components of such compositions can yield some impact improvements without affecting modulus, but results in increased viscosity and reduced processability. A need exists for polymer compositions that have an improved combination of properties, taking into account tensile modulus, impact strength, and melt flow characteristics. It is especially difficult to obtain high tensile modulus, good melt flow characteristics, and good impact strength, in a single composition.
In view of the above, there is a need for a composition having property advantages similar to polycarbonate-polyester blends, but in addition can provide further improvements in tensile modulus without sacrificing impact strength, melt viscosity and other desired mechanical properties.